On the strength of Pine and Spruce Timber. 229 



specimens, which were well seasoned, were carefully selected, and 

 were quite free from splits and knots. Three pieces of each kind 

 of wood were taken, each piece being 9.389 feet in length, 2.75 inch- 

 es in breadth, and 5.5 inches in depth. The distance between the 

 points of support of the pieces under trial, was 7.1 feet. From one 

 end of the beam, one point of support was 0.229 of a foot, or 2.75 

 inches distant, of course the other bearing point was 2.06 feet from 

 the other end. All the above dimensions were chosen from their be- 

 ing proportional to those which will be actually required in the case 

 to which these experiments refer. The load was applied by means 

 of a strong platform suspended from the beam midway between the 

 points of support. Bricks which had previously been accurately 

 weighed, were used as weights. The deflexions were measured by 

 means of an index attached to the centre of the beam, and a scale so 

 supported as to be independent of the rest of the system. The scale 

 was isolated to avoid any irregular motions that might take place in 

 consequence of the great weights it was necessary to employ ; the 

 supports, however, were so securely braced that no motions of the 

 kind were observed. The scale was divided into parts, each of 

 which corresponded to a deflexion in the beam of ^'^th of an inch for 

 one foot in length ; as the distance between the points of support 

 was 7.1 feet, it is easily seen that the length of one of these dimen- 

 sions was 0.177 of an inch. 



This deflexion of ^'^th of an inch to one foot, was chosen as the 

 unit of the scale, in consequence of its having been laid down by 

 practical writers on the subject, as the greatest deflexion of floor 

 beams or joists, that should be allowed in practice.* 



The bricks were slowly and carefully placed upon the platform by 

 two assistants, who kept account of the number in an audible voice. 

 As the beam was gradually bent by the increasing load, the moment 

 when the index pointed to one of the divisions on the scale could be 

 easily observed, at the same time the men, by their counting, gave 

 information of the number of bricks on the platform, which being re- 

 corded opposite the deflexion indicated by the scale, gave the weight 

 producing that deflexion. The men going steadily on, soon brought 

 the index down to another division, when the number of bricks was 

 again recorded, and so on until the deflexion was as great as it was 

 proposed to make it, or until the beam was broken ; in either case 



* See Treileold's Carpentry, p. 30 to 46. 



Vol. XIX.— No. 2. 30 



